The present invention relates to arthroplastic reconstruction of the human joints and more particularly to flexible implant resection arthroplasty of the wrist joint.
In recent years, silicone implants have been successfully employed for the restoration of function of the joints of the hand affected with rheumatoid arthritis and similar conditions. The procedures developed have generally been found to be more successful than prior attempts to restore motion by soft tissue arthroplasties and by the use of metal implants. Due to the shortcomings of prior conventional operational procedures to correct deformities of the wrist joint, flexible implants for this specific joint were developed. Proper function of the wrist joint is necessary for proper function of the hand. A stable and mobile joint is necessary for the proper transmission of muscle forces and for the normal moving and grasping of objects by the hand encountered in normal activities.
Aseptic necrosis and/or arthritis of the carpal bones, either primary or secondary to trauma, is a frequent cause of disability of the wrist joint. Surgical treatment of conditions of the wrist joint have included intercarpal fusion, wrist fusion, local resection, proximal row carpectomy, bone grafting, radial styloidectomy, radial shortening or ulnar lengthening, and soft tissue interposition arthroplasty. Fusion procedures do not provide optimum results since the stability, power and mobility of the wrist is affected even though pain is relieved. Local resection procedures, which involve the removal of an irreversibly pathological bone, are complicated by migration of adjacent carpal bones in the space left by the resection. This results in instability in the wrist joint. Metallic and acrylic implants for the replacement of carpal bones were not satisfactory due to problems relating to progression of the arthritic process, migration of the implant, breakdown of the material and absorption of bone due to hardness of the material inserted.
As a result of the shortcomings of such operative procedures, intramedullary stem silicone rubber implants were developed to replace the lunate bone of the carpal row. The implants were designed to act as articulating spacers capable of maintaining the relationship of adjacent carpal bones after excision of the lunate while preserving mobility of the wrist.
An initial attempt to develop a lunate implant resulted in an implant having essentially the same anatomical shape as the bone being replaced. This implant was developed through exhaustive anatomical shaping and sizing of cadaver bones and roentgenographic studies of a variety of hands. The lunate implant was provided in progressive sizes and concavities were more pronounced then the lunate bone replaced in an attempt to increase stability. A stabilizing stem was formed integral with the implant and fitted into the intramedullary canal of the triquetrum bone.
A second form of lunate implant was developed having a deeper concavity at the distal surface of the implant in an attempt to obtain a better fit around the head of the capitate and therefore obtain increased stability. This increased concavity was not totally satisfactory since impingement with the ligaments of the carpace resulted. Initial silicone implants were essentially anatomically reproduced equivalents to the bones being replaced. These implants included multifaceted and angled and curvilinear surfaces which represented mean averages of approximately 72 different measurements made on each of over one hundred lunate bones. It was believed that an anatomically correct implant including a deeper concavity on the distal surface which articulates with the capitate bone, would result in the most stable arthroplastic reconstruction.